In the context of technical systems for the treatment of compressed gases the use of cooling circuits to reduce the temperature of the gas in order to separate it from its moist component is known.
These cooling circuits typically comprise a compressor, a condenser, a throttling member and an evaporator which exchanges heat with the fluid being treated in order to reduce its temperature.
In the cooling circuits used in systems for drying moist air it is desirable to control the quantity of heat exchanged by the cooling circuit on the basis of the temperature and the flow of the incoming air that has to be dried. In addition to this it will be readily understood that in these applications the parameters of the air which has to be treated readily change on the basis of working conditions or over the period of a day.
The cooling circuits, which are typically dimensioned on the basis of the maximum required load, will exchange an excessive quantity of heat when the system is operating under reduced load.
This excessive heat exchange gives rise to two main disadvantages—an excessive reduction in the temperature of the gas which has to be treated and a parallel waste of energy due to the fact that the work of the compressor is not consequently reduced. In this respect it will also be understood that in a system of this type the operating parameters, such as for example the pressure increase brought about by the compressor or the heat exchanges taking place in the condenser and the evaporator, cannot be varied freely but are defined by the design characteristics of the system. Also there is no possibility of switching the compressor off and then switching it on again at short intervals, as a non-negligible period of time is required between stopping and re-starting the compressor.
One of the ways used to control the heat load produced by the dryer in relation to the demand for dried compressed air comprises providing a loss of head in the cooling fluid upstream of the compressor.
A by-pass branch equipped with a throttle device towards which the cooling flow is diverted after a suitable valve has been switched is used for this purpose. These systems are typically provided with a control unit that activates the by-pass branch when predetermined conditions, of temperature for example, have been fulfilled, thus enabling the system to operate under a condition of maximum cooling or under a condition of relatively reduced cooling. (By “predetermined” is meant determined beforehand, so that the predetermined characteristic (e.g., conditions) must be determined, i.e., chosen or at least known, in advance of some event.) The use of such by-pass branches increases the complexity of the circuit, however, and as a consequence also increases its overall dimensions.
Furthermore the head loss introduced in the by-pass branch cannot always be controlled precisely and therefore does not allow the cooling capacity of the system to be accurately managed, given that the production process for manufacturing the valve/capillary complex involves intrinsic manufacturing difficulties.
In such applications provision for the use of valves which comprise an integrated by-pass branch, such as for example that described in patent JP-H10-62018, is also known.
The technical problem underlying this invention is that of providing apparatus for drying gas which is structurally and functionally designed to make it possible to overcome the abovementioned disadvantages in relation to the known art.